Currently no device is available to automatically, continuously and chronically monitor blood pressure extravascularly. Sphygmomanometers are used to externally monitor blood pressure through the use of an external cuff. In common hospital parlance, stations having what are called inaccurately `dynamap` systems (probably this misnomer is derived from the Johnson & Johnson "DINAMAP" (R) patient monitor systems, which use various blood pressure cuffs) automate these measures for discrete data point analysis. In either system type, the inflatable cuff or other pressure monitoring apparatae are bulky, impede blood flow and require operating personnel to make measurements. As a result these external systems are limited in usefulness to less than 24 hours in common usage. Numerous intravascular and paracorporeal automated pressure sensors have been developed to automate blood pressure monitoring of critically ill patients in hospital settings and for surgical patients. Typically these are composed of a moveable or dispensable membrane surface that by its associations with an electrical sensor produces a signal indicative of the pressure on the membrane. Not only is the usefulness of such devices limited to acute situations where access to the insides of a blood vessel is available, but the mechanical configurations are complex. Accordingly such devices are only able to provide blood pressure readings for a very limited period of time, and in circumstances of intense patient care, like in a hospital setting.
Using currently available internal to the circulatory system systems, at present time there is no good method for chronically measuring blood pressure on the left side of the circulatory system without actually placing a device in contact with the blood. This of course presents a site for thrombogenesis and the possibility of subsequent stroke. If no sensor is placed directly in contact with the blood the challenge is then sensing blood pressure through an arterial wall without introducing errors due to the structure of the arteries supporting all or part of the pressure load.
Further, there is no good present method for continuously sensing over a long period of weeks or months, even including devices which activate a mechanical occluder or cuff so as to provide data beyond mere systolic and diastolic values.
Perhaps the most advanced pressure sensor at the present time is described in some detail in U.S. Pat. No. 5,564,434, incorporated herein by this reference in its entirety. However, this blood pressure sensor is designed for dwelling in the heart of the patient on the heart's right side. Thus any thrombogensis created by the artificial material presence in the blood stream would have limited capacity to damage the patient that is, could not cause a stroke because any thromboses thrown by the device would end up in the patients lung. Thus this patent highlights the difficulty in achieving left side blood pressure measurements.
Other prior systems for attempting to meet some of the requirements described just above include U.S. Pat. No. 4,256,094 issued to Kapp et al, and incorporated herein by this reference in its entirety. This Kapp teaching requires a fairly complex mechanical system including a liquid pump and reservoir and programmable controller for cuffing or occluding the blood flow in the artery, difficulties which are obviated completely by the present invention.
External devices include those described in U.S. Pat. No. 3,926,179, and three which describe a watch mounted external device, U.S. Pat. Nos. 4,802,488; 4,799,49, and 4,269,193 all four hereby incorporated herein by this reference in its entirety. Accordingly, there is a need for a device to enable the continuous chronic monitoring of patient blood pressure automatically and at low cost. To provide such a device without the requirement for vascular access and which could safely monitor the left side of the vascular system as well as the venous system would be of no small additional benefit. It is also an advantage to be able to provide additional devices for deploying sensors chronically to other vessels in the body for sensing other physiologic conditions(e.g. phlebitis).
Such devices as are described herein can be applied to monitoring patients with hypertension without cumbersome discrete point analysis over long terms with many hospital or clinic visits. Dosage accuracy can be enhanced with continuous long term monitoring of blood pressure for administration of hypertensive medications. It is also helpful for interventions to many disease processes such as diabetes, renal and neurologic disease, internal medicine and transplant patients, and any condition where surveillance of patient compliance could be helpful. Not only can continuous systolic, diastolic and pulse pressure monitoring be done with a minimally invasive implant, but additional or just different physiologic signals can be monitored, leaving wide open the scope of application of devices based on this invention.
Thus, the applicability of this invention is not limited to sensing blood pressure however. It should be recognized right from the start that the invention described herein can be used to obviate the use of many sensors which otherwise would require implantation into an active artery or vein system.
For example in U.S. Pat. No. 5,409 (also incorporated in its entirety by this reference) the blood flow is measured using permanently implantable lead within a vein adjacent to an artery. However, using our inventive fixture, flow, temperature, pressure, pulse rate, an even blood oximetry, as well as any other measurement that needs to be taken by a sensor next to the blood flowing through a artery or a vein can be accomplished using a device based on the inventive concepts described herein.
By providing accurate, continuous monitoring of patient blood pressure and other physiologic measures, a profile of patient status during activities of daily living and over prolonged intervals can accurately depict the patient's true hemodynamic health status over months of use. Such automatic monitoring circumvents patient compliance and operator compliance issues which are problematic in the use of external devices. Particularly, the fixture with sensors concepts described herein can be applied to peripheral, internal and neurologic blood and other fluid pressures, flow and so forth. Carotid arterial blood pressure, pulmonary venous blood pressure and cerebral ventricular pressure associated with hydrocephalous are just three examples. The device could be used to monitor the formation of transudate and exhudate fluids, such as in conditions of subcutaneous edema. The device can of course be useful as a research tool, and may find many uses in veterinary medicine and monitoring.